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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

127

FIG. 4

SODIUM NITRATE  (CHILI  SALTPETRE)

graduated, connected* by rubber tubing. Mercury
is poured into B and forced into A by opening
the tap r and raising B ; in this way A is filled with
mercury (care being taken that no air bubbles
remain along the walls of the tube) to the tap,
which is then closed.

From 0-35 to 0-45 gram of the finely powdered
nitrate (which gives not less than 100 and not
more that 130 c.c. of NO) are placed in the funnel
i in which it is shaken with about 0-5 c.c. of hot
water until dissolved. Tube B is then lowered
and the tap r carefully opened, so that the solu-
tion, but no air, enters A. The funnel is washed
with not more than I c.c. of hot water, which is
also cautiously introduced into A. Finally about
15 c.c. of pure cone, sulphuric acid are run into A,
which is shaken vigorously to induce the reaction
between nitrate, sulphuric acid and mercury, by
which the whole of the nitrogen of the nitrate is
converted into nitric oxide. After the lapse of at
least half an hour, the tube B is raised until the
mercury is at the same level in A and B, the
volume of the gas being read, and also the tem-
perature and barometric pressure.

The volume of the gas (V) at o and 760 mm. is given by the formula,

vp

V = r-.;---------7-r, where v is the volume of the gas in the nitrometer,

760(1 + 0-00367 2)                                              5

p the atmospheric pressure and t the temperature.   The amount of NaN03
in the quantity of nitrate taken is equal to 0-0038 times V.

2. INDIRECT METHOD. The moisture, insoluble matter, chlorine and
sulphuric acid are determined by the ordinary methods, the last two con-
stituents being calculated as NaCl and NaaS04. The sum of the percentage
of these four ingredients is then subtracted from 100, the remainder being

the percentage of NaN03.

* *
*

Pure sodium nitrate contains 16-5% of nitrogen, while the commercial
products for fertilising purposes generally contain about 15%. The mean com-
position of the Chili saltpetre coming to Europe is :

Sodium nitrate         .......    94-96%

Sodium chloride       .......    about i%

Sodium sulphate      ....,,.     0-5%

Insoluble matter      .         .         ,         .         .         .                ,,     0-2%

Moisture ..,.,..,,     2%

Among the impurities of importance in sodium nitrate is perchlorate (harm-
ful), which may be present in proportions varying from 0-3 to 5-6%, but is
usually about i% ; the percentage of chlorate varies from o-i to i. Commer-
cial sodium nitrate may be adulterated with salts almost devoid of fertilising
value, such as sodium sulphate, and samples containing 20-40% and even 60%
of this salt have been met with.neous substances have been estimated.    The methods to